1. Field of the Invention
The present invention relates generally to an improved method and apparatus for tracing a plurality of transmission lines from a first location to a second location. Specifically, the present invention is useful for simultaneously tracing a plurality of transmission lines contained within a telecommunications cable.
2. Prior Art
Modern copper telecommunications cables typically contain as many as 600 twisted wire pairs ("line pairs") and may extend several miles in length. Often it becomes necessary to monitor the performance of a given line pair or a number of line pairs within a telecommunications cable. In order to reduce the cost and the time required to trace line pairs, it is highly desirable to be able to trace several line pairs simultaneously.
Apparatuses for tracing line pairs within telecommunications cables are well known in the art. A typical apparatus employs a signal generator which applies a square wave signal to a single line pair. The square wave signal is typically on the order of 5-10 volts in amplitude and has a frequency within the range of 400-1500 Hz. The signal may be continuous or may be switched between two frequencies to add a "warble" sound which is easier for an operator or technician to detect.
In operation, the signal generator is connected to one end of the line pair to be traced and at the opposite end of the cable a high input impedance amplifier is held in close proximity to the line pairs. When the amplifier is close to the actual line pair carrying the square wave signal, the signal is capacitively coupled to the amplifier and becomes audible. The audible signal is then used to identify a particular line pair.
Typically in the prior art, if another line is to be traced, the signal generator must first be disconnected from its current line pair and connected to the next line pair to be traced. Having to switch the square wave generator for each line pair to be traced (each "traced line pair"), is very time consuming particularly when the traced line pairs are part of a telecommunications cable several miles in length.
More recently, devices capable of generating multiple-frequency sequences have been employed in situations where several lines are to be traced. It has been found that the use of such quasi-melodic multi-tone sequences facilitate the technician being able to distinguish between signals and, accordingly, between lines.
The apparatus disclosed in U.S. Pat. No. 5,557,651, which is owned by the Assignee of the present application, is capable of simultaneously tracing a plurality of line pairs by the application of multiple frequency sequences. The disclosed apparatus comprises a signal generator capable of generating at least one signal and a number of switches for operatively coupling the signal to one or more of a number of line pairs. In the preferred embodiment, the signal generator is capable of outputting signals of different frequency in the audio range which can be detected and used by the technician to easily distinguish between line pairs.
Although such an apparatus and corresponding method is effective for tracing multiple line pairs, there is a practical limit to the number of lines that can be simultaneously traced. While in theory it might be possible to generate almost limitless combinations of tones, it becomes difficult, if not impossible, for the technician to identify and distinguish the increasingly complex sequences. Thus, there continues to exist a need in the art for a method and apparatus that will permit simultaneous tracing of a virtually unlimited number of transmission lines.
It is also known in the art to produce signals which simulate speech for use in the evaluation of voice transmission systems in telephony. To that end, signal generators have been provided which produce a signal approximating speech. Such a signal generator is disclosed in U.S. Pat. No. 4, 449,231. The disclosed signal generator is adapted to produce a signal which accurately simulates the syllabic rate of real speech. It has been found that this type of accuracy is necessary in order to properly evaluate the performance of a voice transmission components which may degrade and affect the overall performance of a voice transmission system.
The prior art discloses an apparatus for generating a signal which precisely simulates speech which is used to test voice sensitive components. The prior art does not disclose the application of synthesized speech to a transmission line at a first location for detection at a second location. Thus, although signal generators for simulating a speech signal are known, it is not known to utilize synthesized speech as a means for simultaneously tracing multiple transmission lines from a first location to a second location.
The present invention overcomes the shortcomings associated with the prior art apparatuses for tracing multiple lines by providing an apparatus and method that transmits easily recognizable synthesized speech over a plurality of transmission lines to be traced.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for tracing a plurality of transmission lines from a first location to a second location.
It is a further object of the invention to provide a method and apparatus for simultaneously tracing a plurality of transmission lines from a first location to a second location.
A further object of the invention is to provide a method and apparatus which allows one traced line to be easily distinguished from any other traced line.
Another object of the invention is to provide a method and apparatus that allows the human ear to be used to easily distinguish one traced line from any other traced line.